TSA1203

Application information

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Figure 24. External reference setting

8.3

Driving the differential analog inputs

The TSA1203 is designed to deliver optimum performance when driven on differential

inputs. An RF transformer is an efficient way of achieving this high performance.

Figure 25 describes the schematics. The input signal is fed to the primary of the transformer,

while the secondary drives both ADC inputs. The common mode voltage of the ADC (INCM)

is connected to the center-tap of the secondary of the transformer in order to bias the input

signal around this common voltage, internally set to 0.46V. It determines the DC component

of the analog signal. Being a high-impedance input, it acts as an I/O and can be externally

driven to adjust this DC component. The INCM is decoupled to maintain a low noise level on

this node. Our evaluation board is mounted with a 1:1 ADT1-1WT transformer from Mini

circuits. You might also use a higher impedance ratio (1:2 or 1:4) to reduce the driving

requirement on the analog source.

Figure 25. Differential input configuration with transformer

1k

Ω

TSA1203

VIN

VINB

VREFM

VREFP

external

reference

VCCA

330pF

4.7

μF

10nF

TS821

TS4041

1.2V

TSA1203

VIN

VINB

INCM

50

Ω

33pF

330pF

470nF

10nF

Analog source

1:1

ADT1-1

channels

I or Q